1. Field of the Invention
The present invention relates to manufacturing technology for a semiconductor device, more particularly, to a system for evaluating a design of a mask, an exposure system, a method for evaluating a design of a mask, a method for manufacturing a semiconductor device, and a mask.
2. Description of the Related Art
In a manufacturing process for a semiconductor device, a layout design to implement functions and specifications of the semiconductor device is developed in a design process, and a photomask (hereinafter, referred to as a “mask”) is fabricated. In wafer processing, semiconductor wafers are manufactured using the mask. Subsequently, in an inspection process, the functions and performance of circuits of the semiconductor wafers are inspected. When the inspection reveals a fault such that a desired function or performance cannot be achieved or the like, a design pattern causing the fault is modified in the design process, and the mask is modified.
In the wafer processing after the modification of the mask, and in a lithography process for the mask before modification (hereinafter, referred to as an initial mask) and the mask after modification (hereinafter, referred to as a modified mask), a semiconductor wafer using the initial mask and another semiconductor wafer using the modified mask are separately exposed. These semiconductor wafers are processed under the same conditions in the other manufacturing processes. In the inspection process, the semiconductor wafer manufactured using the initial mask and the semiconductor wafer manufactured using the modified mask are inspected and compared. An evaluation is performed to determine whether the modified mask has fixed the fault of the semiconductor wafer fabricated using the initial mask as expected, and whether the modified mask has caused another fault or degraded the wafer, or the like. When the modified mask improves the wafer, wafer production using the initial mask is changed to wafer production using the modified mask. On the other hand, when the modification does not provide the expected results, the modified mask is further modified. This means that the yield of semiconductor devices in the manufacturing process is increased by repeating the mask modification and inspection.
However, in the wafer processing, semiconductor wafers have manufacturing variations. When the semiconductor wafer fabricated using the initial mask and the semiconductor wafer fabricated using the modified mask are inspected and compared, device characteristics sometimes depend more on the manufacturing variations caused in the wafer processing, than the improvement of the design due to the mask modification. In such a case, it has been difficult to evaluate the improvement of the design due to the mask modification.